Navigating Asteroid Deflection: Avoiding the “Keyhole” to Earth Impact
The European Space Agency’s (ESA) Hera mission, launching in December 2026, will build upon the success of the DART mission by investigating the aftermath of its impact on the asteroid system Didymos and its moonlet, Dimorphos. While DART’s impact successfully altered Dimorphos’ orbit, scientists are now focusing on a more subtle, yet critical, aspect of asteroid deflection: avoiding so-called “gravitational keyholes.”
These keyholes are small regions in space where a planet’s gravity can subtly alter an asteroid’s trajectory. Even a minor change in an asteroid’s orbit can, over time, steer it onto a future collision course with Earth. While Didymos poses no immediate threat due to its size, understanding keyholes is vital for protecting against other potentially hazardous asteroids.Simply nudging an asteroid isn’t enough; inadvertently sending it through a keyhole merely delays a potential impact, making it a future certainty.
“If the asteroid passes one of these keyholes, its movements through the solar system will direct it to the path that causes it to hit the earth in the future,” explains rahil Makadia, a researcher involved in this work.
The challenge lies in identifying the optimal impact point on an asteroid to minimize the risk of sending it through a keyhole. Each location on an asteroid’s surface yields a different probability of altering its orbit in a way that leads to a future impact. Makadia’s team has developed techniques to map these probabilities, using the DART mission as a foundational guide, while acknowledging that each asteroid’s unique characteristics require tailored analysis.
[Image of a probability map of the keyhole from the asteroid Bennu, with a crosshair indicating the location on the surface that minimizes impact danger after deflection. The map shows gray limits representing uncertainty in targeting.] Credit: Rahil Makadia
Accurate assessment requires detailed knowledge of the asteroid’s shape, surface features (hills, craters), rotation, and mass. Ideally, this facts would be gathered by a dedicated space mission providing high-resolution images and data. Though, time constraints – particularly when dealing with newly discovered threats – may necessitate relying on ground-based observations.
“Fortunately,all of this analysis,at least at the preliminary level,it is possible to use land -based observations,even though the meeting mission is preferred,” Makadia notes.
By predicting an asteroid’s future path following a kinetic impact and identifying the most dangerous trajectories, scientists can pinpoint the safest location for intervention. This approach allows for not just deflection, but a calculated course correction that actively prevents future impact scenarios, safeguarding Earth in the long term.
“With this probability map, we can encourage asteroids from going while preventing them from returning to the path of impacts, protecting the earth in the long run,” Makadia concludes.
This research, detailed in a paper titled “Selection of Keyhole Based Sites for the impact of the Kinetic Asteroids near-earth” (Makadia et al., 2025), was presented at the EPSC-DPS 2025 conference and is funded by a NASA Space Technology graduate Research Possibility (NSTGRO) award (NASA Contract No. 80NSSC22K1173).
